This invention relates to a process for producing a single crystal film, and more specifically to a process for producing a single crystal film by epitaxy.
The epitaxial growth technology is extensively used in the manufacture of various single crystal films for diverse applications, such as semiconductors, optical elements, magnetic parts, and magnetooptic elements. For the desired crystal growth it involves the contact of liquid or gaseous material with the surface of a crystal substrate having a lattice constant close to that of the epitaxial to be grown. In this way, a high quality single crystal-film can be made. For example, magnetic garnet, a well-known material for magnetooptic devices, e.g., Faraday rotatably is produced by liquid-phase epitaxial growth (LPE) on a single crystal substrate, such as (Ca,Mg,Zr)-substituted GGG single crystal, so as to form thereon a film .mu.m or more in thickness. The method uses a liquid-phase material and effects its crystal growth.
When such a thick film is required recessed frequently develop between the substrate and the single crystal film, causing strains which, in extreme cases, crack the film. It has been believed possible to avoid this problem by ensuring as close an agreement as possible between the lattice constant of the crystal substrate and that of the crystal film. However, mere agreement in the lattice constant does not solve the problem satisfactorily because, in fact, other parameters including the chemical compositions, thicknesses, and thermal expansion coefficients of the substrate and the single crystal film have a bearing upon the phenomenon. It has also been proposed that two types of films having lattice constants conforming to each other at different temperatures are alternately superposed but this method requires many steps and is time-consuming.